Alpha-synuclein seeds in olfactory mucosa of patients with isolated rapid-eye-movement sleep behaviour disorder

Isolated REM sleep behaviour disorder is an early-stage alpha-synucleinopathy in most, if not all, affected subjects. Detection of pathological alpha-synuclein in peripheral tissues of isolated REM sleep behaviour disorder patients may identify those progressing to Parkinson9s disease, dementia with Lewy bodies or multiple system atrophy, with the ultimate goal of testing preventive therapies. Real-Time Quaking-Induced Conversion provided evidence of alpha-synuclein seeding activity in cerebrospinal fluid and olfactory mucosa of patients with alpha-synucleinopathies. Aim of this study was to explore Real-Time Quaking-Induced Conversion detection of alpha-synuclein aggregates in olfactory mucosa of large cohort of subjects with isolated REM sleep behavior disorder compared to Parkinson9s disease and controls. This prospective bicentric case-control study was performed between October 2017 and December 2018 at the Medical University of Innsbruck, Austria, and the Hospital Clinic de Barcelona, Spain. Olfactory mucosa samples obtained by nasal swab in 63 patients with isolated REM sleep behavior disorder, 31 matched Parkinson9s disease patients and 59 matched controls were analysed by alpha-synuclein Real-Time Quaking-Induced Conversion in a blinded fashion at the University of Verona, Italy. Median age of isolated REM sleep behavior disorder patients was 70 years, 85.7% were male. All participants were tested for smell, autonomic, cognitive and motor functions. Olfactory mucosa was alpha-synuclein Real-Time Quaking-Induced Conversion positive in 44.4% isolated REM sleep behavior disorder patients, 41.9% Parkinson9s disease and 10.2% controls. While the sensitivity for isolated REM sleep behavior disorder plus Parkinson9s disease versus controls was 40.9%, specificity was high (89.8%). Among isolated REM sleep behavior disorder patients with positive alpha-synuclein Real-Time Quaking-Induced Conversion, 78.6% had olfactory dysfunction as compared to 21.4% with negative alpha-synuclein Real-Time Quaking-Induced Conversion, p<0.001. The extent of olfactory dysfunction was more severe in positive than in negative alpha-synuclein Real-Time Quaking-Induced Conversion olfactory mucosa isolated REM sleep behavior disorder patients (p<0.001). We provide evidence that alpha-synuclein Real-Time Quaking-Induced Conversion assay enables the molecular detection of neuronal alpha-synuclein aggregates in olfactory mucosa of patients with isolated REM sleep behavior disorder and Parkinson9s disease. Although the overall sensitivity was moderate in this study, nasal swabbing is attractive as simple, non-invasive test, with a potential of use as screening test to identify subjects in the prodromal stages of alpha-synucleinopathies. Further studies are needed to enhance sensitivity, and better understand the temporal dynamics of alpha-synuclein seeding in the olfactory mucosa and spreading to other brain areas during the progression from isolated REM sleep behavior disorder to overt alpha-synucleinopathy.